Question

cos(x/3)cos(x/3)=1/2[1+cos(2x/3)] is this true or false?

Answer 1

Have you a table of trig identities?
Hint: replace every instance of x/3 with y. Do you then see a familiar trig identity?

Answer 2

yes its part of the product to sum identities right?

Answer 3

Look again, please. Hint: cos y cos y = ?

Answer 4

I still don't understand

Answer 5

Look in your table of trig identities for an identity for (cos x)^2. There's also an identity for (sin x)^2 that has the same form except for sign.

Answer 6

ohhh cos^2x=1+cos2x/2 right?

Answer 7

cos^2x=1+cos2x/2 would be fine with parentheses, not so fine without:

cos^2x=(1+cos2x)/2 right?

Answer 8

yes, so than the answer would be false. correct?

Answer 9

If you're going to do a lot through OpenStudy, try learning Equation Editor. It's a gem!

Explain how you arrived at that conclusion, please.

Answer 10

\[\cos^2x=\frac{ 1 }{ 2 }(1+\cos 2x)\]

Answer 11

is an example of how much clearer this identity is when done in Equation Editor.
Why do you feel that the original statement is false?

Answer 12

If the original is \[\cos2x=1/2(1+\cos2x)\] than dividing by 3 would make it false right?

Answer 13

sorry meant to put the cos squared not 2x

Answer 14

I see. All the more reason to learn to use Equation Editor. Bet you'll like it once you've tried it. OK. Now I'd agree with your response.

Answer 15

So i was correct with the statement that the answer is false?